How Do I Know If I Have Ulcerative Colitis?

Lots of people get stomach cramps and diarrhea. But if you have these symptoms a lot, and they’re severe (extreme cramping, bloody diarrhea), you need to see your doctor. It’s possible you may have ulcerative colitis.

This is a disease of the large intestine or colon. There’s no known cause or cure, but the sooner you get it diagnosed, the quicker you can begin treating the symptoms.

But first you’ve got to get tested.

Doctors can do a wide range of tests to figure out if you’ve got ulcerative colitis.  It may take a series of them to rule out other problems.

Blood and Stool Tests

A blood test can show if you have anemia, which is a symptom of ulcerative colitis. Anemia happens when your red blood cells decrease and there aren’t enough of them to carry adequate oxygen to your tissues. A blood test will also help identify or rule out other infections. 

The blood test can also detect an increase in white blood cells, a low level of the protein albumin, and an elevated C-reactive protein level - all indications of inflammation in your body.

When you go to the doctor’s office, they will take a little of your blood and send it off for analysis. The results will come back anywhere from a couple of days to several weeks later.

A stool test may be ordered to rule out infection. Learn more about stool testing.


You might need a sigmoidoscopy to find out if you have ulcerative colitis. This is a common and routine procedure that takes between 15 and 20 minutes. Your doctor will use a sigmoidoscope to look at your rectal lining and lower large intestine, or colon.

A sigmoidoscope is a long, flexible tube about a half-inch in diameter. It has a light and a small camera on the end of it. Your doctor inserts it into your rectum so they can look at parts of the large intestine. You may be given medicine to help you relax while they do it.


Your doctor will be able to see your intestinal tissue immediately, detecting inflammation and bleeding, and may be able to tell if you have ulcerative colitis or another problem.

You will probably be asked to drink a liquid laxative the night before the test to clean out your bowel so the doctor can clearly see your colon lining.

You should be able to leave right after it’s over. If you had medicine to relax, you’ll need someone to drive you home. Find out more on what to expect during a sigmoidoscopy.



Another way to diagnose ulcerative colitis is a colonoscopy.

This is also an outpatient procedure, which means you can go home when it’s done. It usually takes between 30 minutes to an hour.  You’ll have to drink a liquid laxative the night before to clean out your bowels. This is because your large intestine must be clear for a successful test. Your doctor will give you instructions on how to prepare the day before.

Your doctor will use a flexible tube called a colonoscope to look at your entire colon. They can also take a biopsy, or tissue sample if they need to. This exam can help determine the severity of ulcerative colitis and Crohn’s disease, as well as distinguish between the two diseases.

During the test, a long, thin colonoscope is inserted into your rectum and moved up through your large intestine. You may get a sedative to help you relax. If you do, you will need someone to take you home after it’s done. Get more information on the basics of a colonoscopy.

X-Ray and CT Scan

Your doctor might order an X-ray to make sure you don’t have another kind of problem, like a perforated colon.

Or you might need a CT scan. It helps detect any complications from ulcerative colitis or rule out other conditions that are similar.

Like the other tests, you’ll get ready for the CT scan the night before. Again, your doctor will give you instructions. They usually involve drinking only clear liquids after midnight and eating nothing for 4 hours before the test.

You may need to drink something called a contrast solution and/or have it injected into a vein, right before the test. The CT scan could take between 15 minutes to an hour and your results should be available within 24 hours. Learn more about imaging tests for digestive diseases.

WebMD Medical Reference Reviewed by Minesh Khatri, MD on August 24, 2020



Crohn’s and Colitis Foundation of America: “What is Ulcerative Colitis?” and "Diagnosing Crohn's Disease and Ulcerative Colitis."

CDC: “Diagnosis and Testing for Valley Fever (Coccidioidomycosis).”

Cleveland Clinic: “Diagnostics and Testing.”

Merck Manual Professional Version: “Ulcerative Colitis.”

Merck Manual Consumer Version: "Ulcerative Colitis."

National Health Service England: “Ulcerative colitis-Diagnosis.”

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